PRACTICAL. RESPONSIVE. EXPERT ENGINEERING CONSULTANTS SINCE 1985
Category

Resources

Can Scaffolds Support This?

By | Blog, Resources, Scaffold Bracing, Scaffold Components, Scaffolding | No Comments

Spring is in the air, the birds are chirping and scaffolds are being built. Can life get any better? It used to be that contractors feared winter in the northern regions of North America. Cold temperatures, snow, wind and generally miserable conditions prompted owners and contractors to curtail outdoor activities. That was then; now construction charges ahead, fearless and courageous against even the nastiest of weather. Once again science and progress has prevailed! Improved, clothing, materials, equipment and methods allow construction to continue in any environment.

 To facilitate these activities, it was common to enclose supported scaffolds against the weather. But times have changed; cold weather isn’t the only reason to enclose scaffolds. Containment of debris, tools and workers are now common reasons to enclose scaffolds. Enclosures are also used to advertise, block the work activities from pedestrians and even hide the workers who might be gawking at the pedestrians. Enclosing supported scaffolds is now a year around activity in all areas of North America, on all types of projects in all types of conditions.

Unfortunately, workers have false perceptions concerning supported scaffolds that are enclosed, including the perception that the forces on enclosed scaffolds are not as severe in summer as they are in winter; the perception that using open netting results in lower forces than using solid material; that no additional measures must be taken when a scaffold is enclosed and; site conditions have little effect on an enclosed scaffold.

The truth of the matter is that all scaffolds must be designed by a qualified person, that is, someone who can demonstrate the ability to properly design a scaffold, whether it is enclosed or not. Since designing for wind forces is a necessarily complicated matter, it is common that the qualified person for this design work is a Professional Engineer qualified in such activities. Of course, anyone can take a shot at the design (and unfortunately it is often the case), but the results can be fatal due to a gross underestimation of the forces developed by the wind. So, what is so complicated about wind design? Here are a few factors that must be considered:

Wind Forces

It is absolutely true that the force applied to a scaffold and its enclosure from the wind can be calculated. Short of a meteor falling out of the sky, there is no such thing as a “freak act of nature.” Those who argue so because their scaffold fell over need to be retrained. More accurately, an enclosed scaffold can be designed for a certain maximum wind speed; if the wind is expected to be higher than the design speed, either the scaffold must be dismantled, the enclosure removed, or additional measures must be taken to ensure the stability of the scaffold.

Wind Speed

Obviously, the wind velocity (speed) is the main factor in determining wind forces on a scaffold. However, choosing the correct wind speed for a specific location isn’t that easy. Although wind charts have been developed for North America that indicate maximum design wind velocities, choosing the correct velocity is just the starting point. In fact, there are numerous areas of the continent that have “special wind regions” that require additional investigation to determine the expected wind velocity. One example is along the east side of the Rocky Mountain range, extending from Montana down through Colorado and into New Mexico. At certain times of the year, Chinook winds, that is winds that drop down the east slopes of the mountains, reach as high as 100 mph. Similar winds, called the Santa Ana winds, occur in southern California. These winds don’t occur throughout the year; if your enclosed scaffold is erected during the right time of the year you don’t have to design for these winds; but watch out if the job is delayed and the scaffold is still standing when a Chinook wind hits!

Stability Ties

The key to scaffold success is to adequately design the scaffold and its connection to the adjacent structure. While U.S. federal OSHA and other agencies specify the minimum tie requirements for supported scaffolds, the tie spacing most likely will be grossly inadequate for any substantial enclosed scaffold. While #9 or #12 wire may suffice for a connection of an unenclosed scaffold, it typically is never adequate for an enclosed one. In other words, the ties for an enclosed scaffold must be designed for the anticipated tension and compression loads that are expected to occur. For those who choose to wing it and do something such as doubling up the ties should expect to see their scaffold take wing and fly like a kite. Keep in mind that it is not uncommon to have ties (and the adjacent structure) designed to hold several thousand pounds or more.

Adjustment Factors

When a qualified person designs an enclosed scaffold, he or she must consider these factors:

  • The height of the scaffold
  • The geographical location of the scaffold
  • The location of the scaffold relative to the surrounding structures
  • Surrounding Structures
  • Shape of the Scaffold/Structure (e.g. round or square)
  • Local Wind History
  • Partial or Full Enclosure
  • New construction or demolition
  • Existing structures—are the windows open or closed?

Time of year

This is not a complete list but it gives an idea of the potential complexity of the analysis and design.

Enclosure Porosity

Porosity is the fancy word for how many and how big are the holes in your enclosure material. If you are using netting, the holes can be quite small or they can be big. If the holes are over 2 inches in diameter, such as plastic fencing, porosity can be considered. Otherwise, the prudent scaffold designer will consider the netting as a solid material for the simple reason that the holes can become plugged. Snow and ice can easily plug the most porous netting in winter while sawdust, sand, asbestos (why you would use netting to try to contain asbestos is the more important question – you really need retraining!), stucco, plaster and other fine materials will also have an adverse effect on the airiness of your material regardless of the time of year.

While this article doesn’t cover all the factors that must be considered by the qualified person when designing an enclosed scaffold, it offers a glimpse into the complexity of the situation. Merely “doubling up the ties” and “this is the way I have always done it” is not a prudent approach; it just shows you are lucky. And while being lucky may work in craps or roulette, it has no place in the design of an enclosed supported scaffold. Is your life worth a throw of the dice?

Concrete Formwork – Under Pressure!

By | Blog, Forming | No Comments

Anyone who has worked in the construction industry is likely all too familiar with the term or feeling – “Under Pressure.” In this article I am focusing on concrete formwork engineering pressure, that is.  This article is not going to provide you with a ten step list to have a more peaceful construction related career. I will give you one generic management bite, and that is, “in construction do not let the urgent less important stuff squeeze out the important but less urgent stuff.” Now that is over, I can write about real physical pressure.

For engineering and physics purposes, pressure is simply a mass/weight divided by an area. Fluid pressure builds with the height of fluid. If a submarine goes too deep in the ocean, the fluid pressure can eventually crush the hull. Fluid pressure is calculated by simply multiplying the densify of the fluid by the depth (or height of fluid above). Back to the submarine, the pressure at 10 feet below water is 624 psf, at 1000 ft, you are at a pressure of 62,400 psf. This is also why the 10 ft long snorkel has not taken off in the vacation resorts, your lungs are not strong enough to suck in air past a depth of a couple feet.

Water is easy to visualize but not what I’d call a “common construction material”. However, soils and concrete are commonly designed with the same principle. Concrete has as a fluid has a density of about 150 lbs per cubit (larger than water), so a four foot tall wall form with wet concrete is going to have a pressure of around 600 psf at the bottom of the form. Soil has a typical fluid density of around 130 lbs per cubic foot, so a wall holding back four feet of wet fluid soil is typically modeled as having a pressure of around 520 psf at the bottom of the wall. So, all soil is not fluid like water, therefore geotechnical engineers typically account for this by providing an equivalent fluid pressure for the design. Typical values are between 30-60 lbs per cubic foot, although higher values can occur, especially, if expansive soils conditions exist. So, holding back 10 feet of soil is similar to holding back 8-10 feet of water. Holding back concrete with a height of 10 feet (all fluid) is similar to holding water with a height of 20 feet. This explains why so many forms blowout if not designed!

Remember, similar to you feeling the pressure of stacks of papers / task pile on your desk or mind, concrete, water, and soil increase in pressure with height or depth! A kiddy pool with only 1 ft of water is not a dangerous thing, but a concrete form with 4 ft of wet concrete has some significant pressure and think twice before you fill up that 20 ft tall column form or use plywood and 2x4s to hold back the slope!

Existing Structure Shoring

By | Blog, Resources, Shoring | No Comments

Shoring existing structures can be a tricky business and the older the building, the trickier it can become.  Many older structures do not have drawings of the existing construction and if they do, they are not always reliable.  Many buildings go through generations of remodel with additions, renovations and improvisations that are not always documented properly.  Without proper documentation, it is sometimes difficult to determine the load bearing members in an existing building and this makes it difficult to shore.  If you can’t figure out where the loads are concentrated, you can’t figure out how to safely and economically support anything.

When undertaking the task of existing structure shoring you should consider consulting an engineer – and I don’t just say that because I happen to be an engineer!  The peace of mind that you get from entrusting this work to an engineer far outweighs the risk of liability if something goes wrong during the shoring operation. 

Things that your engineer will need to know before starting a shoring plan include the type of work being performed, the boundaries of work, distance to any excavation, dimensions of the building and location of load bearing members.  Other pertinent information includes the dead load of the supported area and any anticipated live loads – for example, will an office building remain occupied or is your customer trying to keep the parking garage operational during construction?  Depending on the scope of the job, snow and wind loads may also need to be taken into account.  Be certain to consider any special circumstances like required access openings in the shoring plan and work sequencing that would affect the standing shores.  Drawings, schematics and photographs can be provided to convey most of this information but, in some cases, it is easier and most cost effective for the person designing the shoring plan to visit the site.

If an existing structure is improperly shored, there is danger of damaging the building or of a collapse.  Providing as much accurate information as possible to your shoring designer will help to minimize risk and ensure the most accurate and economical design.  Don’t take chances, if in doubt get a professional engineer involved and maximize your chances of shoring success!

Fall Protection – The Full Package

By | Blog, Fall Protection, OSHA Standards & Regulations, Resources, Safety Hazards | No Comments

It has been said that the best solution for fall protection is to not fall, but as falls account for several deaths on construction sites, it turns out this plan doesn’t work out and will make OSHA very grumpy. This topic may be stale news to the salty veterans who have been around the block a time or two but I would be willing to bet that there are very few who consider all aspects of a fall protection every time they don their harness.

Whether you are the engineer designing the plan or the contractor whose life relies on the plan, there are several aspects of fall protection that need to be considered. The most familiar components of fall protection are the personal fall arrest system and the anchor which the system is attached to. Most anyone who has needed to utilize fall protection in their line of work knows that OSHA requires you to use a personal fall arrest system and be connected to a suitable anchor which is capable of supporting 5,000 pounds or be designed by a qualified person. In addition a fall protection user must consider the anchor location in relation to the work area, the fall distance and a rescue plan which are just as important and easier to overlook.

After determining the personal fall arrest system and a suitable anchor, next, consider the work area in relation to the fall protection anchor: It is always a good practice to keep the fall protection system as close to 90 degrees to the edge of the fall hazard as possible. This will limit the amount of swing in the event of a fall reducing the risk of the worker swinging into an object below.

Next, consider the fall distance to prevent a worker from hitting a lower level or an obstruction below as they fall. This aspect of fall protection has the highest variability and can change with each setup. The fall distance can be as little as a few feet if using a self-retracting lifeline attached to a rigid anchor to upwards of 20 feet with some horizontal lifeline applications.

Finally, any fall protection plan is pointless without a way to rescue the poor soul hanging from the system. The fact of the matter is that the fall is not the only way to cause injury and/or death. The sustained mobility of being suspended and the potential for the harness to restrict blood flow can cause serious issues if the worker is not rescued within a reasonable amount of time.

A well designed and implemented fall protection plan must consider all of these aspects. Fall protection may or may not be your bread and butter, however when you need it, considering only some of the aspects could turn into a very bad day. All good ideas start with a plan but without the follow through you’re just a guy hanging there hoping on a dream.

FAQ’s ABOUT FALLS

By | Blog, Resources, Uncategorized | No Comments

A lot has been said about falls and fall protection. The U.S. Federal Occupational Safety & Health Administration, OSHA, has emphasized fall hazard awareness and increased enforcement of the fall protection regulations for years in the hope that deaths and major injuries due to falls in the workplace can be reduced. Manufacturers and suppliers are complementing the OSHA emphasis by offering a plethora of products that can be used to keep employees from falling. Or, more accurately, to keep employees from falling from heights to levels below in such a manner that they get injured or killed.

Due to the complexity of fall protection, it is not a simple procedure to provide personal fall protection equipment in such a way that it will protect an employee in all situations all the time. Confusing the matter is the inaccurate information, conflicting codes and interests, and a whole bunch of misconceptions about fall protection. Here are a few of the more frequently asked questions (FAQS)

What’s a personal fall arrest system? A personal fall arrest system (PFAS) consists of a full body harness, a shock absorbing lanyard or self-retracting lanyard, a vertical lifeline or horizontal lifeline, and an anchor. Alternatively, the lanyard can be attached directly to an anchor, eliminating the lifeline.

Is it true that I can use either a guardrail system or personal fall arrest system when working on a supported scaffold such as a frame or systems scaffold? That is true although the guardrail will be much more effective unless you are using the fall arrest system for fall restraint.

What is fall restraint? Fall restraint is using a personal fall arrest system to keep you from going off the edge of an exposed platform edge. It’s like hooking up the employee to a leash.

Why is a guardrail system more effective than a PFAS? A guardrail system keeps you on the platform or floor while a PFAS catches you after you have decided to leave the platform or floor.

I went bungee jumping once and found it to be exhilarating. Does one get the same thrill from falling off a floor while wearing a PFAS? I don’t know—I haven’t done either one although I want to jump off a bridge attached to a rubber band—sounds like fun. Falling from heights utilizing a PFAS, on the other hand is a whole different experience. While it is often perceived that no injury will occur due to a fall, the truth is quite the opposite. While there are those who experience no injury, typical injuries include severe bruising and intestinal damage. Frankly, the only thing worse than falling while wearing a PFAS is falling without a PFAS.

That doesn’t make sense: people use PFAS daily and I don’t hear of any injuries. What gives? The fact of the matter is that employees utilize/wear PFAS but very, very few actually use it. In other words, although employees wear harnesses and are attached to anchors, they rarely actually use the harness because they don’t fall from heights. Consequently, since they don’t fall, they don’t get hurt.

I have been told that my PFAS anchor has to hold 5,000 pounds unless it is designed by a qualified person, that is someone who knows how to design the anchor and system. Is this true?
Yes it is. The OSHA regulations and other codes require that the anchor you use has to be “capable of supporting at least 5,000 pounds per employee attached, or shall be designed, installed and used as part of a complete PFAS which maintains a safety factor of at least two and under the supervision of a qualified person.” [29 CFR 1926.502(d)(15)]

Are you telling me that before I attach my lifeline or lanyard to an anchor I must have someone determine it can hold 5,000 pounds? Yes.

Come on, no one does that. Everyone eyeballs the chosen anchor and estimates its strong enough. You mean I cannot do that? That is correct: OSHA says you cannot do that.

But it works; I mean that is what everyone does so isn’t it okay? It works because you don’t fall and therefore you never actually use the anchor! Just because you hook off to something that you call an anchor does not an anchor make. In other words, just because it looks good doesn’t necessarily mean it’s going to work. While not recommended, you must jump off the floor to see if your anchor will work.

Why does everyone get away with guessing as to the strength of the anchor? That’s easy; the regulation isn’t enforced. Besides, all the safety folks are happy if the guy is “tied off.” Luckily we don’t have too many employees jumping or falling off floors.

Isn’t tying off the same as utilizing PFAS? No way. You can tie off to anything, including yourself. Properly utilizing a PFAS means that you have selected an anchor that will support 5,000 pounds or you have tied off to an anchor designed by a qualified person in compliance with the mandatory OSHA regulations.

And what are those mandatory regulations? Here are a few: Limit the freefall to 6 feet; stop within 3.5 feet, (known as the deceleration distance); limit the force on the body to 1,800 pounds; and the most important, don’t hit the surface below.

That sounds complicated; is it? Yes, it can get very complicated to design a system that provides 100% fall protection and be in compliance with all of the applicable codes and OSHA regulations. Fortunately, the fall protection equipment manufacturers have done an incredible job of consistently developing new products that can be used to assist employers in protecting employees from fall hazards. It is amazing the changes that have occurred since I first got into the business many years ago. Unfortunately, too many employees lack the training to use the equipment properly. Fortunately, very few employees ever get the opportunity to actually use their PFAS!

How do I obtain the training to utilize and maybe use my PFAS correctly? There are numerous seminars that offer fall protection training. However, I suggest first contacting the manufacturer of your equipment since it should know its products. To learn about the applicable regulations, select a seminar that fits your needs, such as user, inspector or competent person. And finally, verify that the instructor is qualified to teach the seminar.

The ABCs of an Efficient Temporary Wall Bracing Plan

By | Blog, Resources | No Comments

A common concern for many of our clients is to improve the schedule of a job in order to increase revenue and profit. One of the most common ways for a project to gain time in a schedule is to install temporary wall bracing, typically using tilt-up style metal braces. When trying to design the most efficient temporary wall bracing plan, one might want to consider what I like to call the “ABC’s”:

A. Angle: brace capacities are given as an axial load.  After calculating the required horizontal bracing force, the designer must consider how the angle of the brace is going to transfer that horizontal load into an axial load.  This can drastically affect your brace spacing if your brace angle is 60 degrees versus 45 degrees.

B. Bottom: this is typically the main complication of a bracing plan.  The temporary brace resists the overturning of a wall near the top, but there is still the total horizontal load that needs to be resolved at the bottom.  For example, assume that the average load against a 12’ high wall is 5,000 lbs, and it is applied at 1/3 the height (this scenario is similar to backfilling a wall).  The overturning of that backfill is (5,000 lbs) X (12 ft) x (1/3) = 20,000 ft*lbs.  If the brace is installed at 10’, then the required horizontal capacity is (20,000 ft*lbs) / (10 ft) = 2,000 lbs.  However, if the original load against the wall is 5,000 lbs and the brace is only resisting 2,000 lbs, then the bottom of the wall still needs to resist 3,000 lbs.  Typically this is accomplished by installing the slab on grade.  If the slab on grade is not installed, then the designer must analyze the wall itself to resist the load or specify an additional permanent support.  If the wall itself is not sufficient, then it is typically in the best interest of the contractor to install the slab on grade.

C. Connection: connections will need to support shear loads vertically on the wall, horizontally on the slab, and vertically on the slab.  There may be limitations in the existing structure due to substrate thickness, edge/spacing distances, and ground bearing capacity.

By keeping these guidelines in mind, designers maximize the efficiency of bracing for the contractor and the project.

Seismic Retrofit of Existing Buildings

By | Blog, Resources | No Comments

The process of evaluating and designing the retrofit of existing buildings differs from the conventional structural design of new buildings. The current state-of-the-art analysis and design approach for the seismic evaluation of existing buildings is founded on a performance-based philosophy. There are two parts to a performance-based analysis and design.

First, there is the establishment of a performance objective. This answers the question for the designer and the owner, “What degree of damage to the building am I willing to tolerate in the event of an earthquake?” It is not economically feasible to design all buildings to a performance objective that limits all damage or allows the building to remain fully operational and allow immediate occupancy following an earthquake. Therefore, performance objectives exist that allow a certain degree of damage to occur while still protecting life safety and preventing building collapse.

Second, there is the establishment of the seismic demand used in the analysis of the building. Statistical analysis is used to determine the probability of the maximum considered earthquake (MCE) occurring at the building site at any given time. The MCE demand level varies based on the time frame considered and the probability that there will be ground motion at the site that exceeds the MCE (i.e. 5% probability of exceedance in 50 years). Together with these two variables the mean return period of an earthquake can be established (i.e. it can be expected that an earthquake of ‘X’ magnitude, or the MCE, will occur approximately at least every 975 years).

There are various performance objectives and seismic demand levels that may be considered. Any given combination of performance objective and seismic demand level will result in a varied stringency of analysis and design. Combining a strict performance objective (i.e. operational post-earthquake) with an earthquake of relatively long return period (2500 years) will likely result in a robust, yet potentially expensive, design.

In conventional structural analysis and design, the seismic demand used for the design of the seismic force resisting system is reduced by a system-wide Response Modification Factor, R. This coefficient is established based on the ductility of the lateral system selected for design. The R-Factor is intended to act as a representation of the ability of the lateral system to dissipate energy as it flexes, bends, and undergoes inelastic deformation under seismic load.

In the evaluation of existing buildings, the concept of reducing the demand to account for ductility in a system is captured by using component specific m-factors. Rather than reducing the seismic demand, m-factors are applied to scale up the strength or capacity of individual structural elements that experience ductile or “Deformation Controlled” failure. These m-factors vary by component and allow the design professional to apply a uniform seismic demand to the system while modifying the strength of each individual element of the system according to its ductility. This philosophy is ideal for seismic retrofits that require the introduction of an entirely new lateral system or the strengthening of only a few discrete components.

Bridge Overhang Brackets

By | Blog, Resources | No Comments

The proper design of bridge overhang brackets and related falsework is critical. Failure to properly design this falsework can result in partial collapse of the formwork/falsework, damage to the bridge structure and damage to equipment.

Typical bridge construction requires the use of falsework to support workers, the outer edge of the concrete bridge deck, deck screed and sometimes the weight of the concrete barrier.

Falsework is typically anchored to bridge girders by either cast in place steel anchors or by using a cast in place sleeve that allows the use of a threaded rod or coil rod. These anchors can then be fastened to the overhang bracket itself.

Bridge Overhang BracketsCast in place anchors for bridge formwork is available by many suppliers. Some critical things to consider is where the anchor is placed. In box beams for instance, the thickness of the concrete along the top of the box beam may limit the capacity of the anchor. If the capacity of the anchor is limited, then the spacing of the brackets will need to be reduced, resulting in increased costs of equipment and labor. For Bulb Tee beams care also needs to be used when deciding where to place either cast in place anchors or tubular inserts. If cast in place anchors are used, they are typically placed on the edge of the top flange. If the top flange is too thin, then the flange of the girder may be the weak link in the system. Where tubular inserts are used the strength of the girder is less of a concern. When using tubular inserts, a special bracket (typically a steel angle) is required to allow the nuts for the inserted rod to bear properly and prevent bending of the rod.

Supports between the overhang brackets can be made of almost any material. Typically lumber 4×4’s or aluminum beams are used. Additional supports are required under the screed form and may be much larger than the typical supports. The support beams under the concrete deck typically have a tighter spacing than for the walkway.

Where very large screed equipment is used, the equipment typically has a set of multiple wheels. Analysis of the supporting beams for the screed load is a complicated task. Analysis of the multiple screed wheels on a multiple span beam at multiple locations along the beam is required to determine the maximum shear, bending and reaction forces.

On occasion, high winds can cause major damage to the falsework. Wind uplift forces have in the past resulted in the falsework being lifted up and over the edge of the bridge resulting in construction delays and equipment damage. Entire girders may need to be replaced if cast in place anchors were used. To prevent this type of problem multiple methods for holding down the falsework can be used. Brackets can be held down with sandbags, tied with wire to concrete blocks/road barriers or can be anchored to the girders themselves (if allowed).

Plank Criteria

By | Resources, Scaffolding, Scaffolding Platforms | No Comments

There are two criteria that predict the safety of a scaffold platform.  One of the criteria involves the engineering properties of the scaffold unit.  The other criterion addresses the correct installation of the platform.  Correct installation includes proper support, correct positioning to limit spaces between platform units, and the minimum width of the platform.

The Federal Occupational Safety and Health Administration, OSHA, and other agencies, set forth the minimum standards for the installation and use of platform units.  For example, regulations address the minimum and maximum overhang of platform units, the allowable deflection, the space between units, and the distance from the edge of the platform to the work surface and the guardrail system.  These regulations are in the subsection on platforms, 29CFR1926.451(b), and are quite specific.  The regulations address all platforms, including solid sawn wood plank, laminated veneer lumber (lvl), metal fabricated decks, and platforms constructed of structural members and sheathing such as plywood.  These specific regulations ensure that the platform you construct will stay on the scaffold, will be large enough so you won’t fall off the platform, and won’t have any openings that you may fall through.

Engineering properties also predict the safety of the platform.  For manufactured platforms, such as aluminum decks and laminated veneer lumber, the manufacturer indicates the capacity of the product.  For solid sawn plank, determining the capacity is not as straightforward due to varying factors.  These factors include the dimensions of the plank, the specie of tree, what part of the tree is being used, and if the wood has any damage.  How in the world do you determine if the plank is strong enough?  Fortunately, you have help!  Qualified engineers can determine the strength of the plank you are using if the dimensions, the specie of tree, and the quality of the wood are known.  The engineer will also need to know the span of the plank, that is, the distance between supports.  While you can give the engineer the dimensions and span of the plank, the type and quality of the wood is another story.  Unless you cut the tree down yourself, you probably won’t be able to tell if the wood is pine or poplar.  And unless you have learned how to grade lumber, you won’t know if the wood is any good.

How, then, is the grade of the wood determined?  Qualified, trained lumber graders are one method used by lumber mills to determine the strength of wood.  These individuals are trained to determine the various strengths of wood that will come from a tree.  Factors used to determine strength include such things as density (how many rings per inch), the straightness of the grain, and the frequency of knots.  Straighter grain, higher density, and fewer knots will result in a strong piece of wood.  On the other hand, frequent knots and low density will result in a low strength piece of wood.

The engineer relies on the ability of the grader to do his or her job correctly.  The engineer also relies on the accuracy of the stamp to determine precise information for you to use.  The bottom line here is that the information in the grade stamp dictates the accuracy of the engineer’s calculations.  Of course, this information will only be accurate if the plank you use has been graded by a qualified grader, using recognized standards.  If the wood is not as good as the grade stamp indicates disaster will surely follow.

For typical situations, it is recommended that only Scaffold Grade plank be used since this will enhance safety on your scaffold project.  Scaffold Grade plank is a very specific grade of lumber that has a very high strength compared to other commonly found lumber on a construction project.  However, if you choose to use a plank other than scaffold grade, it must be engineered for proper use.  This is the only way you will be safe and in compliance with the regulations.

Do not take chances with solid sawn wood plank.  A grade stamp from a recognized grading agency is your guarantee of accuracy.  High strength lumber is not cheap.  Neither is a worker’s life.  If the board breaks, there is no back-up.